function myfun(){
    let form=document.getElementById('form')
    let username=document.getElementsByName('username')[0]
    
  
    if(username){
        let usernameValue=username.value
        if(usernameValue.length>0){
            return true
        }
        let labletext=document.getElementById('labletext')
        labletext.value=''
        labletext.value='请输入用户名！！'
        return false

    }
    
    return true
        

     

}



